1. Field of the Invention
This invention relates to the field of security, and in particular to the protection of content material via watermarking.
2. Description of Related Art
Watermarking is becoming an increasingly popular technique for protecting content material. A watermarking process embeds an indelible mark into the content material that is configured to be imperceptible during a conventional rendering of the content material. For example, an audio recording is embedded with a watermark by adding material to the audio recording in such a manner that the added material is spatially masked when processed via a conventional audio playback device.
The watermark that is applied to the content material is determined to be irremovable from the content material, so that a rendering device will always be able to detect watermarked material. In this manner, a rendering device can be configured to deny rendering to watermarked material, absent some evidence that the user is authorized to render the watermarked material. For example, U.S. Pat. No. 6,209,092, “METHOD AND SYSTEM FOR TRANSFERRING CONTENT INFORMATION AND SUPPLEMENTAL INFORMATION RELATED THERETO”, issued 27 Mar. 2001 to Johan P. M. G. Linnartz et al, presents a technique for the protection of copyright material via the use of a “ticket” that controls the number of times the protected material may be rendered, and is incorporated by reference herein. If the rendering device detects the presence of a watermark, the ticket is checked to determine whether this rendering exceeds the limited number of authorized renderings. In an example embodiment, the ticket forms the watermark.
Watermarks are preferably designed to be irremovable from the watermarked material. In an effective watermarked object, the watermark cannot be removed without introducing substantial damage to the watermarked object. In the example of an audio recording that is protected by a watermark, attempts to remove the watermark will generally introduce audible distortion to the playback of the previously-watermarked material.
As watermarking becomes more prevalent, so too will attempts to remove watermarking with minimal damage to the protected material. With the ease of communication and distribution provided by the Internet, once a hacker determines how to overcome a particular watermark, it can be expected that the process for removing the watermark will become commonly available, thereby obviating the protection provided by the watermark. This problem will be particularly devastating if current attempts to “standardize” on one watermarking process are successful, and a process for removing this standard watermark is discovered.